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Long term effects of smoking on physical fitness and lung function: a longitudinal study of 1393 middle aged Norwegian men for seven years

^a Department of Medicine, Central Hospital of Akershus, N-1474 Nordbyhagen, Norway

Correspondence to: Dr Erikssen.

Abstract

Objective: to study association between smoking habits and long term decline in physical fitness and lung function in middle aged men who remained healthy.
Design: Baseline and follow up measurements performed during 1972-5 and 1980-2 respectively.
Setting: National University Hospital of Oslo, Norway.
Subjects: 1393 men aged 40-59 at baseline who were all healthy at baseline and at follow up.
Main outcome measures: Forced expiratory volume in one second and physical fitness (defined as total work done during a symptom limited bicycle ergometer test divided by body weight.
Results: Initial fitness was substantially lower among 347 persistent smokers than among 791 persistent non-smokers (1349 J/kg v 1618 J/kg), as was initial forced expiratory volume (3341 ml v 3638 ml). Mean (95% confidence interval) decline in fitness over 7.2 years was 217 (185 to 249) J/kg among smokers compared with 86 (59 to 113) J/kg among non-smokers (P<0.001). Corresponding declines in forced expiratory volume were 271 (226 to 316) ml in smokers and 116 (85 to 147) ml in non-smokers (P<0.001). Differences between smokers and non-smokers remained practically unchanged after adjustment for age and level of physical activity. Changes in fitness and forced expiratory volume among 199 men who had stopped smoking mimicked the findings for persistent non-smokers, and 56 men who started smoking presented findings close to those of persistent smokers.
Conclusion: Decline in physical fitness and lung function among healthy middle aged men was considerably greater among smokers than among nonsmokers and could not be explained by differences in age and physical activity.

Introduction

Physical performance is an important predictor of mortality from cardiovascular causes and from all causes in men^{1 2 3} and is mainly determined by the combined function of the cardiovascular and respiratory systems. Extensive data show that smoking considerably accelerates the sequential decline in lung function,⁴ but little is known about the long term effect of smoking on physical performance. Thus, whereas cross sectional data indicate lower physical performance and response to training in smokers than in non-smokers,^{5 6 7 8 9 10 11 12} no study has to our knowledge reported prospective long term data on change in physical performance in relation to smoking habits.

The present study investigated the association between smoking habits and seven years' change in physical fitness and forced respiratory volume in one second in middle aged men who remained healthy.

Subjects and methods

All apparently healthy men aged 40-59 who were employed in five companies in Oslo, Norway, were invited to participate in a survey that entailed a cardiovascular examination (August 1972 to March 1975). "Apparently healthy" implied absence of any known or suspected heart diseases, diabetes, cancer, hypertension treated with drugs, and miscellaneous diseases described in detail elsewhere.^{1 13} Of 2341 eligible men, 2014 (882 smokers and 1132 nonsmokers), accepted the invitation. An average of 7.2 years later (January 1980 to December 1982), 1757 of the 1933 men who were still alive by 31 December 1982 participated in an identical re-examination. Of these 1757 men, 364 were excluded because they had started treatment with antihypertensive drugs, developed symptoms or signs of coronary heart disease, had a stroke, developed diabetes, developed cancer, or were unable to conduct the second exercise test. This left 1393 men who were healthy according to the initial inclusion criteria and were eligible for the present study. Of the 176 men (1933-1757) who did not respond, 47 (29 smokers, 18 non-smokers) were severely diseased, 47 (24 smokers, 23 non-smokers) found their travelling distance too long, and 82 (51 smokers, 31 non-smokers) did not answer two mailing requests (later data indicated that most of these were diseased at the time of the second survey).

Examination

All examinations took place in the morning at the National University Hospital of Oslo (Rikshospitalet), and the subjects had fasted for 12 hours and had not smoked for at least eight hours beforehand. None was taking drugs, and none had intercurrent illnesses when examined. Table I shows the components of the examination. Detailed data on smoking and physical activity were obtained during interviews. The men were grouped as smokers or non-smokers--baseline non-smokers were labelled as such regardless of previous smoking habits. Men were labelled as physically active if they exercised for at least 30 minutes twice weekly to the level of breath shortness and sweating.¹ Combining baseline and follow up smoking data allowed subclassification of subjects as persistent non-smokers (n=791), persistent smokers (n=347), baseline smokers who had quit (n=199), and baseline non-smokers who had started (n=56).

TABLE I--Components of physical examination
----------------------------------------------------------------------------
1 Detailed case history, including questionnaire on physical activity and
   interview about physical activity during leisure hours
2 Complete clinical examination
3 Measurements of height and weight
4 Spirographic measurements (peak expiratory flow, forced expiratory
   volume in one second, and vital capacity)*
5 Series of blood tests (including a lipid profile)
6 X ray examination of heart and lungs
7 Resting electrocardiogram
8 Electrocardiogram during symptom limited exercise test on electrically
   braked Elema bicycle ergometer
----------------------------------------------------------------------------
*The highest value of two measurements (performed after careful instruction
and one trial attempt).

The exercise test was conducted on an electrically braked Elema bicycle as described previously and was continued until exhaustion if it was not stopped earlier for specified safety reasons.¹ The starting load was 5.87 kJ/min and the load was increased by 2.94 kJ/min at intervals of six minutes. Physical fitness was defined as working capacity divided by body weight, with working capacity defined as the cumulated work performed during the symptom limited exercise test. Forced expiratory volume in one second was measured with a Bernstein spirometer.¹⁴

STATISTICAL METHODS

Possible group differences were tested with two sided t tests at a 5% significance level. Multivariate regression analysis was applied for studying simultaneously the influence of several factors on change in physical fitness and forced expiratory volume in one second.

Results

Table II shows the values of clinical, laboratory, and physiological parameters for the groups of subjects at baseline and follow up. Body weight, systolic blood pressure, maximal heart rate during exercise, and serum triglyceride concentration showed small but significant and systematic differences between groups and sequential changes. Other differences were minor and not significant. All differences between smokers and non-smokers were graded according to the number of cigarettes smoked (detailed data not shown).¹⁴

TABLE II--Mean (SD) values for some clinical, laboratory, and physiological variables at baseline and
follow up by smoking habits among 1393 healthy middle aged men
--------------------------------------------------------------------------------------------------------
                                        Unchanged smoking habits                Changed smoking habits
--------------------------------------------------------------------------------------------------------
                                                                        Stopped          Started
                                      Non smokers       Smokers         smoking         smoking
                                       (n=791)          (n=347)         (n=199)         (n=56)
--------------------------------------------------------------------------------------------------------
Age (years):
 Baseline                            49.1 (5.5)        49.4 (5.1)       49.4 (5.3)      49.1 (5.2)
 Follow up                           56.3 (5.5)        56.5 (5.0)       57.0 (5.3)      56.3 (5.3)
Body weight (kg):
 Baseline                            76.8 (9.2)        75.6 (9.8)*      75.8 (9.3)      77.5 (9.2)
 Follow up                           77.4 (9.1)        75.8 (9.8)*      78.4 (9.4)      76.5 (9.1)
Body height (cm):
 Baseline                           177.0 (6.3)       176.6 (6.0)      176.9 (5.8)     178.0 (5.8)
 Follow up                          176.8 (6.3)       176.4 (5.9)      176.7 (5.8)     177.8 (5.8)
Body mass index:
 Baseline                            24.5 (2.8)        24.2 (2.7)       24.2 (2.7)      24.4 (2.5)
 Follow up                           24.7 (2.8)        24.3 (2.7)*      25.1 (2.8)      24.2 (2.5)
Blood pressure (mm Hg):
 Resting systolic:
  Baseline                          129 (17)          125 (16)**       125 (17)        125 (16)
  Follow up                         131 (18)*         128 (16)*        133 (18)        127 (16)
 Resting diastolic:
  Baseline                           87 (10)           84 (10)**        84 (9)          84 (10)
  Follow up*                         88 (10)           86 (10)*         89 (10)         84 (10)
 Maximal systolic:
  Baseline                          215 (21)          211 (22)*        214 (21)        217 (20)
  Follow up                         216 (21)          215 (23)         220 (22)        213 (20)
Heart rate (beats/min):
 Resting:
  Baseline                           62 (10)           59 (8)**         60 (9)          60 (9)
  Follow up                          63 (10)           62 (9)           63 (10)         62 (10)
 Maximal:
  Baseline                          167 (12)          160 (14)***      163 (13)        166 (13)
  Follow up                         161 (11)          152 (13)***      158 (13)        158 (12)
Serum lipid concentration (mmol/l):
 Cholesterol
  Baseline                            6.6 (1.2)         6.7 (1.2)*       6.7 (1.2)       6.6 (1.2)
  Follow up                           6.4 (1.1)         6.6 (1.2)**      6.5 (1.1)       6.4 (1.2)
 Triglycerides
  Baseline                            1.22 (0.71)       1.35 (0.72)      1.30 (0.67)     1.22 (0.71)
  Follow up                           1.37 (0.81)       1.55 (0.74)***   1.49 (0.70)     1.29 (0.72)**
--------------------------------------------------------------------------------------------------------
*P<0.05, **P<0.01, ***P<0.001 compared with persistent non-smokers.

FITNESS

Table III shows the results of the exercise tests, and table IV shows that baseline fitness was significantly higher among non-smokers than among smokers (P<0.001) and that the seven year drop in fitness was significantly lower in non-smokers (9% v 22%, P<0.001). This second difference was greater in the men aged 40-49 than in those aged 50-59.

TABLE III--Total work performed, duration of exercise test, and maximal work load of healthy middle aged
men by smoking habit. Values are means (SD) unless stated otherwise
--------------------------------------------------------------------------------------------------------
                                      Unchanged smoking habits                Changed smoking habits
--------------------------------------------------------------------------------------------------------
                                                                       Stopped          Started
                                    Non-smokers        Smokers         smoking         smoking
                                     (n=791)           (n=347)         (n=199)         (n=56)
-------------------------------------------------------------------------------------------------------
Total work done (kJ)+:
 Baseline                          124 (50)          102 (34)***     112 (43)        122 (41)
 Follow up                         118 (51)           86 (36)***     102 (47)        105 (42)
 Difference                          6 (29)            16 (23)***     10 (24)         17 (27)
 95% Confidence interval of
   difference                           4 to 8          13 to 19        7 to 13         10 to 24
Duration of exercise test (minutes):
 Baseline                           14.8 (4.0)        12.9 (3.1)***   13.8 (3.7)      14.7 (3.4)
 Follow up                          14.1 (4.0)        11.3 (3.6)***   12.7 (4.0)      13.2 (3.7)
 Difference                          0.7 (2.5)         1.6 (2.3)***    1.1 (2.3)       1.5 (2.3)
 95% Confidence interval of
   difference                         0.5 to 0.9        1.4 to 1.8     0.8 to 1.4      0.9 to 2.1
Maximal working capacity (watts)++:
 Baseline                          186 (35)           174 (28)***    180 (31)         189 (27)
 Follow up                         190 (37)           166 (31)***    179 (36)          181 (32)
 Difference                         -4 (27)***          8 (26)         1 (25)           8 (24)
 95% Confidence interval of
   difference                          -6 to -2            5 to 11       -3 to 5           2 to 14
--------------------------------------------------------------------------------------------------------
***P<0.001 compared with persistent non-smokers.
+Sum of all work performed at all exercise levels.
++Maximal load tolerated for at least one minute.

TABLE IV--Physical fitness (J/kg) of healthy middle aged men by smoking habit. Values are means (SD)
unless stated otherwise
------------------------------------------------------------------------------------------------------
                                 Unchanged smoking habits             Changed smoking habits
------------------------------------------------------------------------------------------------------
                                                                     Stopped          Started
                                Non-smokers        Smokers           smoking         smoking
------------------------------------------------------------------------------------------------------
All subjects:
 No of men                       791              347                199              56
 Baseline fitness               1618 (630)       1349 (413)***      1477 (520)     1565 (457)
 Follow up fitness              1532 (639)       1132 (439)***      1307 (593)     1362 (471)
 Difference                      86 (384)         217 (307)***       170 (338)      203 (338)
 95% Confidence interval of
  difference                      59 to 113       185 to 249         123 to 217     114 to 292
Men aged 40-49 at baseline:
 No of men                       437              182                 95             32
 Baseline fitness               1808 (653)       1488 (392)***      1645 (567)     1613 (391)
 Follow up fitness              1761 (659)       1280 (430)***      1546 (654)     1473 (487)
 Difference                       47 (411)        208 (332)***        99 (355)      139 (351)
 95% Confidence interval of
  difference                       8 to 86        160 to 256          28 to 170      17 to 261
Men aged 50-59 at baseline:
 No of men                       354              165                104             24
 Baseline fitness               1384 (513)       1195 (380)***      1324 (423)     1501 (535)
 Follow up fitness              1250 (483)        968 (389)***      1088 (430)     1214 (412)
 Difference                      134 (341)        227 (277)***       236 (308)      287 (307)
 95% Confidence interval of
  difference                      98 to 170       185 to 269         177 to 295     164 to 410
------------------------------------------------------------------------------------------------------
***P<0.001 compared with persistent non-smokers.

For the 1138 men with unchanged smoking habits, multivariate regression analysis was used to test possible influence of age, smoking, level of physical activity and initial fitness on the seven year change in fitness. The analysis showed that high initial fitness and high age were associated with a high reduction in fitness (P<0.001) and that high physical activity was associated with a low reduction in fitness (P=0.039). When these three confounders had been accounted for, the seven year reduction in fitness was 13.6% higher among smokers than among non-smokers (P<0.001).

FORCED EXPIRATORY VOLUME

Table V shows that data for forced expiratory volume in one second showed a similar pattern in relation to smoking habits as physical fitness; that is, non-smokers had higher baseline values and a lower seven year decline.

TABLE V--Forced expiratory volume (ml) in one second of middle aged men by smoking habit. Values are means (SD)
unless stated otherwise
----------------------------------------------------------------------------------------------------------------
                                       Unchanged smoking habits                   Changed smoking habits
----------------------------------------------------------------------------------------------------------------
                                                                               Stopped              Started
                                     Non-smokers          Smokers              smoking              smoking
----------------------------------------------------------------------------------------------------------------
All subjects:
 No of men                            781                 344                 198                   56
 Baseline volume                     3638 (685)          3341 (698)***       3350 (733)          3571 (638)
 Follow up volume                    3522 (704)          3070 (738)***       3204 (791)          3325 (663)
 Difference                           116 (439)           271 (423)***        146 (426)           245 (553)
 95% Confidence interval of
  difference                           85 to 147          226 to 316           87 to  205         100 to 390
Men aged 40-49 at baseline:
 No of men                            433                 182                  94                  32
 Baseline volume                     3830 (679)          3579 (696)***       3537 (734)          3548 (645)
 Follow up volume                    3751 (690)          3354 (687)***       3458 (789)          3521 (638)
 Difference                            79 (449)           225 (409)***         78 (469)           127 (674)
 95% Confidence interval of
  baseline                             37 to 121          166 to 284          -17 to 173         -107 to 361
Men aged 59-59 at baseline:
 No of men                            348                 162                 104                  24
 Baseline volume                     3401 (615)          3074 (599)***       3182 (695)          3467 (626)
 Follow up volume                    3238 (613)          2752 (660)***       2974 (724)          3064 (615)
 Difference                           162 (423)           322 (433)***        208 (375)           403 (269)
 95% Confidence interval of
  difference                         118 to 206          255 to 389         136 to 280          295 to 511
----------------------------------------------------------------------------------------------------------------
***P<0.001 compared with persistent non-smokers.

Multivariate regression analysis of forced expiratory volume in men with unchanged smoking habits showed that high initial expiratory volume and high age were associated with a high reduction in expiratory volume (P<0.001) but physical activity was not associated with change in volume. When the two confounding factors were adjusted for, the seven year reduction in forced expiratory volume was 6.0% higher among smokers than among non-smokers (P<0.001).

Discussion

In the study non-smokers had substantially higher values for physical fitness and forced expiratory volume in one second at baseline than smokers, and these differences had increased at follow up seven years later. By addressing the effect of smoking on lung function and physical fitness only in men who remained healthy, this study grossly underestimates the negative health consequences of smoking. In fact, as we reported previously,¹ we found the same increased mortality and morbidity among smokers that has been reported generally.^{4 15} For example, smoking doubled the risk of dying from both cardiovascular and non-cardiovascular diseases,¹ and non-responders who were diseased were mostly smokers. The results of our present study, however, should be relevant for middle aged men who are generally healthy. In addition the 199 men who stopped smoking during the study and the 56 who started smoking offer a limited opportunity of assessing possible effects of changing smoking habits late in life.

Our data on physical fitness and lung function in relation to smoking are unlikely to be biased because other studies corroborate the smoking related differences we found for other physiological parameters--for example, blood pressure,¹⁶ body weight,^{4 15} maximal heart rate response to exercise,^{12 16} and serum triglyceride concentration.^{17 18} Our spirographic results also agree with reports of more pronounced long term decline in forced expiratory volume in one second in smokers than in non-smokers.^{4 19 20} Moreover, we found that results for men who started smoking during the study mimicked those of persisent smokers while results for men who stopped smoking mimicked those for persistent non-smokers, suggesting that the smoking associated changes in the bronchi^{4 15 19 20} are at least partly reversible even in smokers aged 40-59.

PHYSICAL FITNESS

Various studies--none of which provide follow up data--have indicated a lower physical performance in smokers than in non-smokers.^{5 6 7 8 9 10 11 12} One major cross sectional study, which addressed this aspect by means of symptom limited exercise testing,¹² produced results virtually identical to our baseline findings--that is, smoking being associated with lower heart rate response on all exercise levels, lower maximal heart rate, and lower maximal working capacity. By extrapolating from similar findings of submaximal heart rate (using the Astrand-Ryhming nomogram²¹), one research group erroneously concluded that smokers seemed more fit than non-smokers.²² Our results show that healthy smokers showed a substantially larger decline in physical performance than non-smokers. Men who started smoking seemed to mimic persistent smokers whereas, with due caution for small numbers, men who stopped smoking seemed to show slightly differing patterns depending on their age: those aged 40-49 seemed to benefit from stopping smoking while those aged 50-59 did so only marginally if at all.

Although our spirographic results agree with other reports of the negative effects of smoking,^{4 15 19 20} these observed differences in lung function alone can hardly explain the differences in fitness. Thus cardiovascular factors seem to be the main limiting factors in maximal exercise in healthy subjects, although respiratory muscle fatigue may be the limiting factor to endurance exercise even in athletes.²³ The explanation for our results from the exercise tests is therefore uncertain. One possible explanation might be that binding of carbon monoxide and cyanide to haemoglobin and cytochrome inhibited oxygen delivery and metabolism in smokers. We have no data to support this notion, but the half lives of bound carbon monoxide and cyanide are sufficiently long that the eight hours' abstention from smoking that preceded exercise testing would not have eliminated this possible effect even if all the smokers had abstained from smoking. Conceivably, smoking associated impairment of pulmonary oxygen exchange may also in part explain lower maximum oxygen consumption in smokers than in non-smokers.^{4 16 24} Alternative but speculative explanations are down regulation of adrenergic receptors among smokers²⁵ and long term cardiac damage caused by stimulation of catecholamine by lifelong smoking.^{26 27 28 29 30} Such hypotheses could be tested in populations with a low prevalence of coronary heart disease and a high prevalence of smoking.

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